1. Field of the Invention
The present invention relates to data cryptography, and more particularly, to a cryptographic apparatus for encrypting and decrypting data.
2. Description of the Related Art
Cryptography technology is frequently used to ensure message transmission security. In cryptography technology, a message (hereafter, referred to as plain text) is encrypted at a transmission side and a message (hereafter, referred to as cipher text) is decrypted or decoded at a receiving side. Such an encryption and a decryption of the messages are well known as cryptography technology.
The data encryption standard (DES) is a block unit encryption protocol employed in many nations and American National Standards Institute (ANSI). Also, there are 3-DES, AES and the like as examples of the encryption protocol. In the block unit encryption protocol, various modes, i.e., electronic codebook (ECB), cipher block chaining (CBC), output feedback (OFB), cipher feedback (CFB), and the like are defined. Recently, counter mode and offset codebook (OCB) mode have been suggested.
These various modes can be implemented by individual hardware. However, to implement the various modes in one chip, many gates are required.